Revert "nvk: Enable VK_KHR_shader_subgroup_uniform_control_flow"
This reverts commit ac5d529c. We're failing 4 of the tests:
dEQP-VK.reconvergence.subgroup_uniform_control_flow_ballot.compute.nesting4.1.2
dEQP-VK.reconvergence.subgroup_uniform_control_flow_elect.compute.nesting4.1.2
dEQP-VK.reconvergence.workgroup_uniform_control_flow_ballot.compute.nesting4.1.2
dEQP-VK.reconvergence.workgroup_uniform_control_flow_elect.compute.nesting4.1.2
This is because we aren't guaranteeing re-convergence for loop continues.